Shader "Hidden/GreyScale" {

Properties {
    _MainTex ("Base (RGB)", 2D) = "white" {}
}

SubShader {

    Pass {

        ZTest Always Cull Off ZWrite Off
        Fog { Mode off }

        CGPROGRAM
            #pragma vertex vert_img
            #pragma fragment frag
            #pragma fragmentoption ARB_precision_hint_fastest 
            #include "UnityCG.cginc"

            uniform sampler2D _MainTex;

            uniform float _Strength;

            float4 frag (v2f_img i) : COLOR {

                float4 c = tex2D(_MainTex, i.uv);

                float4 g = (c.r+c.g+c.b)/3.0;

                c.rgb = lerp(c, g, _Strength);

                return c;
            }
        ENDCG
    }
}

 

Fallback off

 

}